databendlabs/databend · error

internal error: entered unreachable code

Error message

internal error: entered unreachable code

What it means

In the materialized-view rewriter's rewrite_aggregate, the code first matched a select item as an aggregate-shaped SelectTarget and then re-matches it as SelectTarget::AliasedExpr; the second match is assumed infallible, so the else branch is `unreachable!()`. If the matched item was actually a SelectStmt::aliased_items / non-aliased target, the assumption is wrong and the rewriter panics.

Solutions

1. Check the preceding filter that selected `selected_group`; extend it to guarantee the item is AliasedExpr.
2. Log the offending select target when the invariant breaks to identify which MV/query shape triggers it.
3. Return None/Ok(false) from rewrite_aggregate for non-aliased targets, falling back to normal (non-MV) query execution.
4. Recreate the MV with explicit aliases for every GROUP BY expression as a workaround.

Example fix

// before
} else {
    unreachable!()
};
// after
} else {
    return Ok(false);
};

// Detect MV rewrite panics and fall back to base-table execution
if err.contains("unreachable code") && uses_materialized_view(query) {
    exec(query_without_mv(query));
}

When it happens

Trigger: Rewriting a query against a materialized view whose GROUP BY matching logic selects an output item that is not SelectTarget::AliasedExpr — e.g. MV definitions with unusual select-item forms (expressions without alias, set-returning items) that slip past the earlier filter.

Common situations: Hit by users querying an aggregate materialized view where the MV's SELECT list contains GROUP BY expressions the rewriter maps by alias; typically after changes to SelectTarget representation or MV binding.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• internal error: entered unreachable code
• internal error: entered unreachable code
• plan in InsertInputSource::Stag must be CopyIntoTable
• internal error: entered unreachable code
• {}

AI-assisted analysis of databendlabs/databend@288d84d76e (2026-09-11). Data as JSON: /api/errors/e631d344dad7ab57. Report an issue: GitHub.

Appendix: source

Thrown at src/query/sql/src/planner/semantic/materialized_view_rewriter.rs:281

                        original_targets.iter().enumerate().find(|(_, target)| {
                            matches!(target, SelectTarget::AliasedExpr { alias: Some(alias), .. }
                                if matches!(group, Expr::ColumnRef { column, .. }
                                    if column.column.name() == alias.name))
                        })
                    });

                let Some((first_output_index, selected_group)) = selected_group else {
                    return Err(ErrorCode::InvalidMaterializedView(format!(
                        "GROUP BY key '{}' is not in the view definition's select list",
                        group
                    )));
                };
                let SelectTarget::AliasedExpr {
                    expr: selected_expr,
                    ..
                } = selected_group
                else {
                    unreachable!()
                };
                let selected_expr_text = selected_expr.to_string();
                // Store a repeated GROUP BY expression only once, under the first matching output
                // name. Every logical output of that expression must reference this same physical
                // column; otherwise later outputs would retain a source expression that does not
                // exist in the MV storage schema.
                let name = output_names[first_output_index].clone();
                for (output_index, target) in original_targets.iter().enumerate() {
                    if matches!(target, SelectTarget::AliasedExpr { expr, .. }
                        if expr.to_string() == selected_expr_text)
                    {
                        self.logical_define_exprs[output_index] = name.clone();
                    }
                }
                aggregate_targets.push(AggregateExprRewriter::target(
                    selected_expr.as_ref().clone(),
                    &name,
                ));

View on GitHub (pinned to 288d84d76e)